This invention relates to a photocurable composition and, more particularly, to a photocurable composition which is especially suitable for forming printing plates.
As a photocurable composition for forming printing plates in the conventional art, there has been, for example, proposed and disclosed in the Japanese Pat. No. 265 544 a photocurable composition comprising a high molecular material, a polymerizable ethylenically unsaturated compound and a photosensitizer which is applied or molded onto substrate to obtain a relief image forming layer of solid state at room temperature. Said relief image forming layer is cured by the application of actinic rays and then the un-cured portion is washed away with aqueous alkali solution to obtain the desired printing plate.
Although said high molecular materials such as cellulose derivatives having oxyacid groups, acrylic polymer having oxyacid group and acidic polyvinyl alcohol have two characteristics that make it possible to keep the photocurable composition at solid state at room temperature and that can allow the un-cured photocurable composition to wash away by using an aqueous alkali solution, they are poor in compatibility with the polymerizable ethylenically unsaturated compound and reduce the photopolymerization velocity at the time of forming printing plate. Further, the printing plate obtained is inferior in respect of several properties such as toughness, flexibility, stiffness, abrasion resistance and water resistance.